Roughened bond coat and method for producing using a slurry

ABSTRACT

A method of providing a roughened bond coat, for example in a thermal barrier coating system, comprises providing an oxidation-resistant plasma-sprayed layer onto a substrate and disposing a slurry overlayer on the oxidation-resistant plasma-sprayed layer. These steps form a roughened bond coat possessing an uneven, undulated, and irregular surface. A roughened bond coat in a thermal barrier coating system reduces de-bonding of the bond coat and a thermal barrier coating layer, which is desirable to maintain the insulation features of the thermal barrier coating system.

This application is a division of application Ser. No. 09/199,062 ,filed Nov. 24, 1998, now U.S. Pat. No. 6,242,050 which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to bond coats. In particular, the inventionrelates to roughened bond coats for thermal barrier coating systems.

Thermal barrier coating systems are used in hot-section components inturbine and turbine components, for example components of jet enginesand gas turbines. The thermal barrier coating system insulates theturbines from high temperatures during thermal cycling. Thermal barriercoating systems include a thermal barrier coating (TBC) disposed on abond coat, which in turn is disposed on a substrate. The thermal barriercoating normally comprises zirconia, for example such as one of astabilized zirconia and a partially-stabilized zirconia (PSZ). The bondcoat typically comprises an oxidation-resistant metallic layer disposedbetween the TBC and substrate (turbine component). The TBC is adhered tothe bond coat typically by mechanical interlocking, so the bond coatprovides oxidation resistant to the substrate and a relatively roughsurface. The bond coat surface generally has Ra (Arithmetic AverageRoughness (Ra) as determined from ANSI/ASME Standard B461-1985) valuesover about 350 mainly by mechanical interlocking. So the function of thebond coat is to provide oxidation resistant to the substrate and arelatively rough surface, preferably with Ra values over about 350microinches, for the TBC to adhere to the substrate. Thus, the TBC isdisposed over the turbine component can provide thermal insulation.

FIG. 1 is a schematic representation of a known thermal barrier coatingsystem 1. A substrate 10 comprises an underlying part of a component,for example a turbine component. A bond coat 12 is disposed on thesubstrate 10. The bond coat is disposed on the substrate 10 by anyappropriate method, for example, but not limited to, thermal sprayprocesses, such as vacuum plasma spray (VPS), air plasma spray (APS) andhyper-velocity oxy-fuel (HVOF) spray processes.

The structure and roughness of bond coat surface 13 are dependent on thespray process. Bond coats deposited by a VPS process are typically denseand free of oxides. Therefore, VPS-applied bond coats provide protectionat high temperatures against oxidation. The VPS application processdisposes fine powders, and thus, VPS-applied bond coats are typicallydense, for example having a density greater than about 90% of itstheoretical density, but have relatively smooth surfaces. Consequently,a TBC does not adhere well to a VPS bond coat.

An air plasma spray (APS) process produces rough bond coats because oflarge powders used in APS. The large powders possess a relatively highheat capacity; however, the APS-applied bond coats contain high amountsof oxides. Also, APS-applied bond coats possess a relatively lowporosity due to the oxidation environment and low momentum of thepowders. Although APS-applied bond coats provide better TBC adhesion dueto their roughness, they are more prone to oxidation because of theirrelatively high oxide levels and relatively low porosity.

Bond coats deposited by HVOF are sensitive to particle sizedistributions. Dense and oxide-free bond coats can be deposited by HVOFusing very lean conditions (low oxygen amounts) and finer particles, forexample particles with a size about −325+10 μm. The surface roughness ofHVOF-applied bond coats is relatively smooth. Rough bond coats can bedeposited by HVOF using coarser powders, for example particles with asize about −230+325, however a low HVOF flame temperature is needed. Thelow flame temperatures result in the bond coat comprising un-meltedpowders, therefore the coating is porous and less dense.

A TBC 14 is disposed on the bond coat 12 and forms a surface 15 againstthe surface 13. The TBC 14 is disposed on the bond coat 12 by anyappropriate process to adhere (bond) to the bond coat. The TBC surface15 and bond coat surface 13 define an interfacial area 16 at theiradjoining surfaces.

Effectiveness of a thermal barrier coating system during thermal cyclingis compromised by de-bonding of the TBC and bond coat, for example atthe TBC and bond coat interfacial area. De-bonding can be caused by atleast one of a poor TBC and bond coat adhesion, and lack ofaccommodation of thermal expansion mismatch between the TBC and bondcoat. The lack of adhesion is characteristic of smooth adjoiningsurfaces where a total surface area is minimal. The thermal expansionmismatch between the TBC and bond coat results from differentcoefficients of thermal expansion of the materials used for thesefeatures. If the difference in coefficients of thermal expansion of theadhered elements is large, one element expands much more than the other,and separation and de-bonding occur at the interfacial areas. De-bondingof the TBC and bond coat is undesirable as the insulation effect of thethermal barrier coating system will be lost at TBC separation.

Therefore, it is desirable to use a very dense and rough bond coat thatprovides oxidation resistance and promotes enhanced adhesion between theTBC and the bond coat. The adhesion between the TBC and bond coat can beincreased by increasing an area at an interfacial area mating surface ofadhered elements. Increasing a roughness of the bond coat provides anincreased area and enhanced mechanical interlocking between the bondcoat and TBC. Increasing a bond coat's roughness also provides anincreased interfacial surface area for accommodation of any thermalmismatch, with respect to non-roughened bond coats.

SUMMARY OF THE INVENTION

Thus, this invention overcomes the above noted deficiencies of knownbond coats and thermal barrier coating systems. The invention provides amethod for providing a dense (for example at least about 95% itstheoretical density), roughened bond coat, for example on a substrate,such as a turbine component, in a thermal barrier coating system. Themethod comprises providing an oxidation-resistant plasma-sprayed layeronto a substrate; and disposing a slurry overlayer on theoxidation-resistant plasma-sprayed layer to form a roughened bond coatpossessing an uneven, undulated, and irregular surface.

A dense, (for example at least about 95% its theoretical density),roughened bond coat is also set forth in an embodiment of the invention.The roughened bond coat comprises an oxidation-resistant plasma-sprayedlayer and a slurry overlayer on the oxidation-resistant plasma-sprayedlayer to form an uneven, undulated, and irregular surface.

Further, a method for providing a thermal barrier coating system isdisclosed in another embodiment of the invention. The thermal barriercoating system comprises a dense (for example at least about 95% itstheoretical density), roughened bond coat and a thermal barrier coatingdisposed on a substrate. The method of providing a thermal barriercoating system comprises disposing a roughened bond coat on thesubstrate and disposing a thermal barrier coating on the roughened bondcoat. The disposing a roughened bond coat comprises providing anoxidation-resistant plasma-sprayed layer onto a substrate and disposinga slurry overlayer on the oxidation-resistant plasma-sprayed layer toform an uneven, undulated, and irregular surface.

A thermal barrier coating system, as embodied by the invention,comprises a dense (for example at least about 95% its theoreticaldensity), roughened bond coat disposed on a substrate and a thermalbarrier coating disposed on the roughened bond coat. The roughened bondcoat comprises an oxidation-resistant plasma-sprayed layer and a slurryoverlayer on the oxidation-resistant plasma-sprayed layer. These layersform the roughened bond coat possessing an uneven, undulated, andirregular surface.

These and other aspects, advantages and salient features of theinvention will become apparent from the following detailed description,which, when taken in conjunction with the annexed drawings, where likeparts are designated by like reference characters throughout thedrawings, disclose embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a known thermal barrier coatingsystem;

FIG. 2 is a schematic representation of a thermal barrier coating systemincluding a roughened bond coat;

FIG. 3 is a flow chart of one method for forming a thermal barriercoating system; and

FIG. 4 is a microphotograph of a roughened bond coat.

DETAILED DESCRIPTION OF THE INVENTION

Roughened bond coats enhance adhesion between a thermal barrier coating(TBC) and a bond coat in a thermal barrier coating system. Roughenedbond coats prevent de-bonding and separation between the TBC and bondcoat of the thermal barrier coating system. A roughened bond coatincreases interfacial mating surface areas of adhered elements, enhancesmechanical interlocking between the bond coat and TBC, and provides foraccommodation of any thermal mismatch between the TBC and bond coat.Accordingly, expansion of elements in a thermal barrier coating systemwith a roughened bond coat does not lend to separation and de-bondingtherebetween. An effect of the roughened bond coat includes an enhancedlife of the TBC in the thermal barrier coating system.

In the following description, material compositions of mixtures areprovided in weight percent unless otherwise expressed. Further,individual compositions are provided in weight percent, unless otherwiseprovided. For example, if a mixture comprises about 70% of Constituent Aand about 30% of constituent B, the percents are in approximate weightpercents. Nomenclature used for compositions is as follows. IfComposition A comprises Ni-23Cr-6AI-0.4Y, yttrium is provided at 0.4weight percent, aluminum is provided at 6 weight percent, chromium isprovided at 23 weight percent, and nickel is provided as the balanceweight percent.

FIG. 2 is a schematic illustration of a thermal barrier coating system100, as embodied by the invention. The thermal barrier coating system100 comprises a substrate 110. A dense roughened bond coat 120, whichpossesses an uneven, undulated, and irregular surface, is disposed onthe substrate 110. A thermal barrier coating (TBC) 130 is disposed onthe roughened bond coat 120. The roughened bond coat 120 comprises anuneven, undulated, and irregular surface 121, which is disposed againsta mating surface 131 of the TBC 130 to define a roughened interfacialsurface area 140. The density of the bond coat 120 is at least about 95%its theoretical density.

The substrate 110 comprises an element to be thermally insulated by thethermal barrier coating system 100. For example, the substrate 110comprises a component such as a turbine component, turbine airfoilblade, bucket, vane, and nozzle (hereinafter “turbine component”). Ifthe substrate 110 comprises a turbine component, an appropriatesubstrate material includes one of a nickel-based superalloy material,an iron-based superalloy material, a nickel-iron-based superalloymaterial, and a cobalt-based superalloy material. The followingdescription refers to a nickel-based superalloy material, however thismaterial is merely exemplary of substrate materials, and is not meant tolimit the invention in any way. Other substrate materials are within thescope of the invention.

The TBC 130 comprises appropriate materials that provide thermalinsulation. For example, but in no way limiting of the invention, theTBC 130 comprises zirconia. The zirconia comprises at least one of astabilized zirconia and a partially stabilized zirconia (PSZ).

The roughened interfacial surface area 140, which is defined by thesurfaces 121 and 131, has a larger interfacial surface area, withrespect to a substantially smooth interfacial area 16 of a known thermalbarrier coating system 1. The roughened interfacial surface area 140permits more contact between the roughened bond coat 120 and the TBC130. This contact provides enhanced mechanical interlocking and adhesionbetween the bond coat 120 and TBC 130.

The roughened bond coat 120 comprises an oxidation-resistantplasma-sprayed layer 122 and a slurry overlayer 124. Theoxidation-resistant plasma-sprayed layer 122 is applied to the substrate110 by an appropriate process, such as by an air plasma-sprayingprocess.

The oxidation-resistant plasma-sprayed layer 122 comprises an oxidationresistant material. An exemplary oxidation resistant material comprisesMCrAIY, where M is at least one of nickel (Ni), iron (Fe), and cobalt(Co), for example Ni-23Cr-6AI-0.4Y (weight percent). Theoxidation-resistant plasma-sprayed layer 122 is applied with a thicknessin a range from about 0.005 inches to about 0.010 inches (about 0.0125cm to about 0.025 cm). The invention describes MCrAIY as NiCrAIY,however this is merely exemplary and not meant to limit the invention inany way.

The roughness of the bond coat 120 is sufficient to increase interfacialsurface areas at the interface, thus reducing de-bonding and increasingaccommodation of thermal expansion mismatches. The bond coat 120, asembodied by the invention, possesses a roughness in a range of about 100microinches (about 2.5×10⁻⁴ cm) Ra (Arithmetic Average Roughness (Ra) asdetermined from ANSI/ASME Standard B461-1985) to about 2000 microinches(about 5.0×10⁻³ cm) Ra. Alternatively, the bond coat 120 possesses aroughness in a range of about 100 microinches (about 2.5×10⁻⁴ cm) Ra toabout 400 microinches (about 1.0×10⁻³ cm) Ra. Further, the bond coat 120possesses a roughness in a range of about 100 microinches (about2.5×10⁻⁴ cm) Ra to about 300 microinches (about 7.5×10⁻⁴ cm) Ra.

The slurry overlayer 124 is formed from a slurry mixture. The slurrymixture comprises at least a first oxidation-resistant powder with afirst melting point, a second oxidation-resistant powder with a secondmelting point that is lower than the first melting point, and anappropriate binder that holds powders and similar materials together.The slurry overlayer 124 is disposed on the oxidation-resistantplasma-sprayed layer 122. For example, the slurry overlayer 124 iscoated onto the oxidation-resistant plasma-sprayed layer 122, such as bya painting process. The combination of first and second melting pointpowders results in a higher density, for example a density of at leastabout 95% of its theoretical density.

Compositions for the slurry overlayer 124 comprise a binder and a metalpowder, where the metal powder comprises various constituents in variousamounts. A first slurry composition, “Slurry A” comprises a mixture ofabout 70% metal powder by weight and about 30% binder by weight. TheSlurry A metal powder comprises about 50 volume-percent NiCrAlY(Ni-23Cr-6Al-0.4Y) and about 50 volume-percent Al-11.6Si (weightpercent).

A second slurry composition, “Slurry B,” also comprises a mixture ofabout 70% metal powder by weight and about 30% binder by weight. TheSlurry B metal powder comprises about 50 volume-percent NiCrAlY andabout 50 volume-percent Ni-60Al-1B (weight-percent).

NiCrAlY is an oxidation-resistant material with a relatively highmelting point (about 1350° C.). Al-11.6Si and Ni-60Al-1B have meltingpoints, about 577° C. and about 850° C., respectively, which are lowerthan that of NiCrAlY. Therefore, Al-11.6Si and Ni-60Al-1B melt beforeNiCrAlY during any subsequent heat treatments of the thermal barriercoating system 100. When the Al-11.6Si and Ni-60Al-1B reacts with theNiCrAlY in the slurry and the material of the oxidation-resistant layer122 re-solidify, they fuse (bond) the NiCrAlY and layer 122 together.The TBC, for example, but not limited to, a ceramic composition TBC, isthen applied to the surface 121 by an appropriate process, such as, butnot limited to, air plasma spraying (APS)

FIG. 3 is a flow chart of a process to prepare a thermal barrier coatingsystem that includes a roughened bond coat, as embodied by theinvention. In step S1, the oxidation-resistant plasma-sprayed layer isdisposed onto a substrate, for example a turbine component. In step S2,the slurry overlayer is disposed on the oxidation-resistantplasma-sprayed layer. The disposing of the oxidation-resistantplasma-sprayed layer and slurry overlayer form a bond coat, when theyare re-acted and fused in a heat treatment of step S3. For example, anexemplary heat treatment comprises heating at about 1200° C. for about 1hr in a vacuum.

In step S4, a TBC is disposed onto the bond coat to form a thermalbarrier coating system. The thermal barrier coating system undergoesoptional heat treatment in step S5. Any optional heat treatments of thethermal barrier coating system occur after the TBC has dried.

Re-solidification after heat treatment causes the melted low meltingpoint powder, such as at least one of melted Al-11.6Si and Ni-60Al-1B,to fuse un-melted high melting point powders, for example NiCrAlYpowder, to the plasma-sprayed layer. The fusing results in an enhancedroughened bond coat since some un-melted powders tend to be located atthe surface of the material as it re-solidifies. The fusing also resultsin enhanced adhesion of the thermal barrier coating system's featuresbecause of the enhances interfacial area.

FIG. 4 is as microphotograph of a roughened bond coat, as embodied bythe invention. As illustrated, a surface of the bond coat is rough andpossesses an uneven, undulated, and irregular surface. A high meltingpoint powder, such as NiCrAlY powder, in the slurry-formed overlayerdoes not melt during heat treatment, since its melting point is higherthan that of the heat treatment. If the heat treatment temperature isabove that of the low melting point powder, such as Al-11.6Si andNi-60Al-1B, these powders are melted, re-acted, and re-solidified.

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements, variationsor improvements therein may be made by those skilled in the art, and arewithin the scope of the invention.

What is claimed is:
 1. A bond coat comprising: an oxidation-resistantplasma-sprayed layer; and a discrete overlayer on theoxidation-resistant plasma-sprayed layer to form an uneven, undulated,and irregular surface, wherein the overlayer is fused to theoxidation-resistant plasma-sprayed layer, and wherein the bond coat hasa density of at least about 95% its theoretical density.
 2. A bond coataccording to claim 1, wherein the oxidation resistant material comprisesMCrAlY, where M is at least one of nickel (Ni), iron (Fe), and cobalt(Co).
 3. A bond coat according to claim 2, wherein the MCrAlY comprisesNi-23Cr-6Al-0.4Y.
 4. A bond coat according to claim 1, wherein theoxidation-resistant plasma-sprayed layer comprises a layer with athickness in a range from about 0.0125 cm to about 0.025 cm.
 5. A bondcoat according to claim 1, wherein the overlayer comprises materialformed from a slurry mixture.
 6. A bond coat according to claim 5,wherein slurry mixture comprises a metal,powder mixture and a binder. 7.A bond coat according to claim 6, wherein the metal powder mixture and abinder comprises about 70% by weight of the metal powder and about 30%by weight of the binder.
 8. A bond coat according to claim 7, whereinthe metal powder mixture comprises a first oxidation-resistant powdermetal powder having a first melting point and a second oxidationresistant powder having a second melting point that is lower than thefirst melting point.
 9. A bond coat according to claim 8, wherein thefirst oxidation-resistant powder metal powder and the second oxidationresistant powder comprise about 50% by volume of the firstoxidation-resistant powder and about 50% by volume of the secondoxidation-resistant powder.
 10. A bond coat according to claim 9,wherein the first oxidation resistant powder comprises MCrAlY, where Mis at least one of nickel (Ni), iron (Fe), and cobalt (Co).
 11. A bondcoat according to claim 9, wherein the second oxidation resistant powdercomprises at least one of Al-11.6Si and Ni-60Al-1B.
 12. A bond coataccording to claim 1, wherein the bond coat is disposed on a turbinecomponent.
 13. A bond coat according to claim 1, wherein the disposingthe metallic material forms the uneven, undulated, and irregular surfacewith roughness in a range from about 2.5×10⁻⁴ cm Ra to about 5.0×10⁻³ cmRa.
 14. A bond coat according to claim 1, wherein the disposing themetallic material forms the uneven, undulated, and irregular surfacewith roughness in a range from about 2.5×10⁻⁴ cm Ra to about 10⁻³ cm Ra.15. A bond coat according to claim 1, wherein the disposing the metallicmaterial forms the uneven, undulated, and irregular surface withroughness in a range from about 2.5×10⁻⁴ cm Ra to about 7.5×10⁻⁴ cm Ra.16. A turbine component, the turbine component comprising: a) asubstrate; and b) a bond coat disposed on the substrate, the bond coatcomprising an oxidation-resistant plasma-sprayed layer disposed on thesubstrate and an overlayer disposed on the oxidation-resistantplasma-sprayed layer, the overlayer being discrete from theoxidation-resistant plasma-sprayed layer and having an outer surface,wherein the outer surface has an enhanced degree of roughness, andwherein the overlayer is fused to the oxidation-resistant plasma-sprayedlayer by heat treating the oxidation-resistant plasma-sprayed layer, theoverlayer, and the substrate.
 17. The turbine component of claim 16,further comprising a thermal barrier coating disposed on the outersurface.
 18. The turbine component of claim 17, wherein the thermalbarrier coating comprises a ceramic material.
 19. The turbine componentof claim 18, wherein the ceramic material is zirconia.
 20. The turbinecomponent of claim 19, wherein the ceramic material is a zirconiaselected from the group consisting of stabilized zirconia and partiallystabilized zirconia.
 21. The turbine component of claim 17, wherein theturbine component is a hot stage turbine component.
 22. The turbinecomponent of claim 21, wherein the turbine component is a hot stageturbine component in an aircraft turbine.
 23. The turbine component ofclaim 21, wherein the turbine component is a hot stage turbine componentin a gas turbine.
 24. The turbine component of claim 21, wherein theoxidation resistant material comprises MCrAlY, where M is at least onemetal selected from the group consisting of nickel (Ni), iron (Fe), andcobalt (Co).
 25. The turbine component of claim 7, wherein the MCrAlYcomprises Ni-23Cr-6Al-0.4Y.
 26. The turbine component of claim 16,wherein the oxidation-resistant plasma-sprayed layer has a thickness ofbetween about 0.0125 cm and about 0.025 cm.
 27. The turbine component ofclaim 16, wherein the outer surface has a roughness of between about2.5×10⁻⁴ cm Ra and about 5.0×10⁻³ cm Ra.
 28. The turbine component ofclaim 27, wherein the outer surface has a roughness of between about2.5×10⁻⁴ cm Ra and about 10⁻³ cm Ra.
 29. The turbine component of claim28, wherein the outer surface has a roughness of between about 2.5×10⁻⁴cm Ra and about 7.5×10⁻⁴ cm Ra.
 30. A turbine component, the turbinecomponent comprising: a. a substrate; b. an oxidation-resistantplasma-sprayed layer; c. a discrete overlayer on the oxidation-resistantplasma-sprayed layer to form an outer surface, wherein the outer surfacehas an enhanced degree of roughness, and wherein the overlayer is fusedto the oxidation-resistant plasma-sprayed layer by heat treating theoxidation-resistant plasma-sprayed layer and the overlayer, wherein thebond coat has a density of at least about 95% of its theoreticaldensity; and d. a thermal barrier coating disposed on the outer surface.31. The turbine component of claim 30, wherein the thermal barriercoating comprises a ceramic material.
 32. The turbine component of claim31, wherein the ceramic material is zirconia.
 33. The turbine componentof claim 32, wherein the ceramic material is a zirconia selected fromthe group consisting of stabilized zirconia and partially stabilizedzirconia.
 34. The turbine component of claim 30, wherein the oxidationresistant material comprises MCrAlY, where M is at least one metalselected from the group consisting of nickel (Ni), iron (Fe), and cobalt(Co).
 35. The turbine component of claim 34, wherein the MCrAlYcomprises Ni-23Cr-6Al-0.4Y.
 36. The turbine component of claim 30,wherein the oxidation-resistant plasma-sprayed layer has a thickness ofbetween about 0.0125 cm and about 0.025 cm.
 37. The turbine component ofclaim 30, wherein the outer surface has a roughness of between about2.5×10⁻⁴ cm Ra and about 5.0×10⁻³ cm Ra.
 38. The turbine component ofclaim 30, wherein the outer surface has a roughness of between about2.5×10⁻⁴ cm Ra and about 10⁻³ cm Ra.
 39. The turbine component of claim30, wherein the outer surface has a roughness of between about 2.5×10⁻⁴cm Ra and about 7.5×10⁻⁴ cm Ra.
 40. The turbine component of claim 30,wherein the overlayer comprises a material formed from a slurry mixture.41. The turbine component of claim 40, wherein the slurry mixturecomprises a metal powder mixture and a binder.
 42. The turbine componentof claim 41, wherein the slurry mixture comprises about 70% by weight ofthe metal powder mixture and about 30% by weight of the binder.
 43. Theturbine component of claim 42, wherein the metal powder mixturecomprises a first oxidation-resistant metal powder having a firstmelting point and a second oxidation resistant powder having a secondmelting point, wherein the second melting point is lower than the firstmelting point.
 44. The turbine component of claim 43, wherein the metalpowder mixture comprises about 50% by volume of the firstoxidation-resistant powder and about 50% by volume of the secondoxidation-resistant powder.
 45. The turbine component of claim 44,wherein the first oxidation resistant metal powder comprises MCrAlY,where M is at least one of nickel (Ni), iron (Fe), and cobalt (Co). 46.The turbine component of claim 45, wherein the second oxidationresistant powder comprises at least one of Al-11.6Si and Ni-60Al-1B. 47.The turbine component of claim 30, wherein the turbine component is ahot stage turbine component.
 48. The turbine component of claim 47,wherein the turbine component is a hot stage turbine component in anaircraft turbine.
 49. The turbine component of claim 48, wherein theturbine component is a hot stage turbine component in a gas turbine. 50.A bond coat for a turbine component, the bond coat comprising: a. anoxidation-resistant plasma-sprayed layer; and b. a discrete overlayer onthe oxidation-resistant plasma-sprayed layer to form an outer surfacehaving an enhanced degree of roughness, wherein the overlayer is fusedto the oxidation-resistant plasma-sprayed layer by heat treating theoxidation-resistant plasma-sprayed layer and the overlayer, and whereinthe bond coat has a density of at least about 95% of its theoreticaldensity.
 51. The bond coat of claim 50, wherein the oxidation resistantmaterial comprises MCrAlY, where M is at least one of nickel (Ni), iron(Fe), and cobalt (Co).
 52. The bond coat of claim 51, wherein the MCrAlYcomprises Ni-23Cr-6Al-0.4Y.
 53. The bond coat of claim 50, wherein theoxidation-resistant plasma-sprayed layer has a thickness of betweenabout 0.0125 cm and about 0.025 cm.
 54. The bond coat according to claim50, wherein the overlayer comprises a material formed from a slurrymixture.
 55. The bond coat of claim 54, wherein the slurry mixturecomprises a metal powder mixture and a binder.
 56. The bond coat ofclaim 55, wherein the slurry mixture comprises about 70% by weight ofthe metal powder mixture and about 30% by weight of the binder.
 57. Thebond coat of claim 56, wherein the metal powder mixture comprises afirst oxidation-resistant metal powder having a first melting point anda second oxidation resistant powder having a second melting point,wherein the second melting point is lower than the first melting point.58. The bond coat of claim 57, wherein the metal powder mixturecomprises about 50% by volume of the first oxidation-resistant powderand about 50% by volume of the second oxidation-resistant powder. 59.The bond coat of claim 57, wherein the first oxidation resistant metalpowder comprises MCrAlY, where M is at least one of nickel (Ni), iron(Fe), and cobalt (Co).
 60. The bond coat of claim 57, wherein the secondoxidation resistant powder comprises at least one of Al-11.6Si andNi-60Al-1B.
 61. The bond coat of claim 50, wherein the outer surface hasa roughness in a range from about 2.5×10⁻⁴ cm Ra to about 5.0×10⁻³ cmRa.
 62. The bond coat of claim 50, wherein the outer surface has aroughness in a range from about 2.5×10⁻⁴ cm Ra to about 10⁻³ cm Ra. 63.The bond coat of claim 50, wherein the outer surface has a roughness ina range from about 2.5×10⁻⁴ cm Ra to about 7.5×10⁻⁴ cm Ra.